1. Field of the Invention
The present invention relates to devices for the self-determination of a person's interpupillary distance.
2. Prior Art
OTC reading glasses have been available for many years. Most have been single vision half-eye designs to enable the wearer to look over the top for distance use, and also different straight top bifocal designs to allow the wearer to view distant images through a plano (zero power) segment without the need for removing the glasses. The problem with current over-the-counter (OTC) reading glasses is that they are not made with customized pupillary distance (PD's) as is done in custom-made spectacles. The PD of prior art bifocal glasses, as currently manufactured, depends on the geometric or mechanical center of the frame itself, wherein the optical center of the lens is centered in the geometric center of the frame. Large frames have large distances between the optical centers of the lenses. A person with a narrow pupillary distance (PD) measurement of, for example, 56 mm., could be wearing OTC reading glasses with 66 mm. optical centers. This creates up to 2 diopters of induced prism effect that would cause eyestrain and discomfort and would be outside of ANSI standards for ophthalmic lenses.
As the age of the population increases, many people with otherwise healthy eyes are becoming presbyopic: a loss of the eyes' ability to see objects close up such as small print and reading materials. Presbyopes currently must get an eye exam in order to acquire glasses having the correct PD because a choice of spectacles having different PD's have not been available OTC, and need to be custom made.
The need for a simple device that can be used to self-determine the PD has been recognized and addressed in the art. For example, Blattberg, in U.S. Pat. No. 5,461,434, discloses a method and apparatus for interpupillary distance measurement. The device includes a frame and a pair of sliders. In use, the sliders are mounted in the frame and adjusted horizontally apart by the user and fixed in that position for later measurement. A bifocal or multifocal optical centering device and method is also described. The optical centering device includes a frame which is attached to a spectacle lens and a slider adjusted therein relative to the user's eye. The position of the slider is then fixed for later measurement.
Edwards et al., in U.S. Pat. No. 5,822,032, discloses a device for measuring the interpupillary distance of the eyes. The device has a frame having a first hole which is positionable at the pupil of the person's left eye, and a disk rotatably mounted on the frame which is rotatable about an axis perpendicular to the face of the frame. The disk has a plurality of second holes which spiral radially outwardly on the disk from the axis. By rotating the disk, one of the second holes is viewable through a window in the frame and positionable at the pupil of the person's right eye. The interpupillary distance (PD) is equal or approximately equal to the distance between the centers of the first and second holes when the holes are positioned at the respective pupils of the person. Numerals representing the PD appear on the surface of the disk through another window in the frame.
While OTC spectacles are currently available in a variety of powers, there is a need for OTC spectacles that are also available in a plurality of PD's for each power. While it is optimal but impractical to provide OTC glasses in all possible PD's, it is both sensible and practical to provide OTC glasses in several PD's (such as, for example, SMALL, MEDIUM and LARGE) for each power so that after a person selects the correct power, the user can further select the glasses having a PD that best fits their interpupillary separation. In the event that such OTC glasses become available in the future, there will be a need for a device that enables a person to easily determine his/her personal PD, in an OTC setting, in order to select OTC spectacles having not only the correct power, but also having a PD that most closely approximates their personal PD.